DENVER—A 20-year government effort to restore the population of an endangered native trout in Colorado has made little progress because biologists have been stocking some of the waterways with the wrong fish, a new study says.

Biologists called the finding a setback and a potential black eye but said there is still hope for restoring the greenback cutthroat trout because at least four pure populations of the fish have been identified.

The three-year study was led by University of Colorado researchers and published online in Molecular Ecology on Aug. 28. The U.S. Fish and Wildlife Service, which is heading the recovery effort, said it is reviewing the findings.

The study said that out of nine populations of fish believed to be endangered greenback cutthroat trout that were descendants of survivors, five were actually the Colorado River cutthroat trout, which look similar but are a separate and more common subspecies.

The other four populations were greenbacks.

The recovery effort by Colorado and federal biologists was thought to be close to its goal of 20 self-sustaining populations of at least 500 fish each. Bruce Rosenlund of the U.S. Fish and Wildlife Service in Denver said federal and state agencies working on restoration believed the fish were found in 142 miles of waterways, including in Rocky Mountain National Park.

Researchers, though, said that based on genetic test results, the greenback cutthroat trout’s range is only 11 miles of streams.

The study said the results imply that the effort has “failed to improve the species’ status.”

Rosenlund said other scientists will read and comment on the research. He said biologists working on restoring the greenback trout want to see “the science played out.”

“The report is just a continuation of different expert input provided to the team for consideration for restoration,” said Rosenlund, the project leader for the agency’s assistance office.

State and federal biologists will continue with other key parts of the recovery program, such as habitat restoration.

Colorado Division of Wildlife spokesman Tyler Baskfield said the research results are a setback but state biologists believe the program will succeed over the long term.

“We’ve been moving fish around in the state since the late 1800s and now the new science comes in and all of a sudden it’s a different playing field,” Baskfield said.

In 1998, officials projected it would cost $634,000 to bring the greenback to recovery, with the money coming from a variety of sources. It wasn’t clear how much of that has been spent. Figures for the recovery project before 1998 weren’t available.

The study’s lead author, Jessica Metcalf, who recently completed her doctorate in ecology and evolutionary biology at the University of Colorado, said scientific advances continue to shed new light on the program. She said there’s reason for optimism about the findings.

“Four of the native populations appear to be pure greenback cutthroat trout,” Metcalf said in an interview from San Francisco, where she was set to present the research Thursday at an American Fisheries Society meeting.

Greenback cutthroat trout were historically found in the drainages of the Arkansas and South Platte rivers in Colorado and a small part of Wyoming. They were declared extinct in 1937 due to overfishing, pollution from mines and competition from nonnative fish.

Researchers said remnant populations were found in the 1950s in tributaries and provided brood stock for fish raised in federal and state hatcheries and released in their native habitat. The fish was added to the federal endangered species list in 1978.

Other federal agencies, including the Bureau of Land Management and Forest Service, have helped with the recovery program. An overall cost estimate wasn’t available.

The greenback, the Colorado River cutthroat trout and the Rio Grande cutthroat trout all evolved in Colorado. A fourth subspecies, the yellowfin cutthroat, is believed to be extinct.

Metcalf said although the greenback and Colorado River cutthroat are closely related, they’ve likely been different subspecies for about a half million years. One of the challenges facing biologists, she said, was the lack of baseline information about the greenback, which was already “in major decline” when first described in detail in the late 1800s.

In June, federal officials rejected efforts to designate the Colorado River cutthroat trout as endangered, citing a substantial increase in the number of known populations.

University of Colorado professor Andrew Martin, the study’s principal investigator, said while the findings might give the recovery program “black eye,” the hope is that biologists and agencies will move ahead on recovering the species before it goes extinct.

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